Abstract
During the development of low or ultra-low permeability oil resources, the alternative energy supply becomes a prominent issue. In recent years, carbon dots (CDs) have drawn much attention owing to their application potential in oil fields for reducing injection pressure and augmenting oil recovery. However, carbon dots characterized of small size, high surface energy are faced with several challenges, such as self-aggregation and settling. The preparation of stably dispersed carbon dots nanofluids is the key factor to guarantee its application performance in formation. In this work, we investigated the stability of hydrophilic carbon dots (HICDs) and hydrophobic carbon dots–Tween 80 (HOCDs) nanofluids. The influences of carbon dots concentration, sorts and concentration of salt ions as well as temperature on the stability of CDs were studied. The results showed that HICDs are more sensitive to sort and concentration of salt ions, while HOCDs are more sensitive to temperature. In addition, the core flooding experiments demonstrated that the pressure reduction rate of HICDs and HOCDs nanofluids can be as high as 17.88% and 26.14%, respectively. Hence, the HICDs and HOCDs nanofluids show a good application potential in the reduction of injection pressure during the development of low and ultra-low permeability oil resources.
Highlights
With the continuous growth in crude oil demand, unconventional oil and gas resources become increasingly significant (Liu et al 2017, 2019)
When the concentration of both hydrophilic carbon dots (HICDs) and hydrophobic carbon dots–Tween 80 (HOCDs) is 0.1 wt%, no obvious agglomeration was observed in the solution, and the particle size was mainly distributed at around 10 nm
It was found that the average particle size of HOCDs was of 8.88 nm and zeta potential is about -6.5 mV, while the average particle size of HICDs was of 12.88 nm and zeta potential is about -36.5 mV
Summary
With the continuous growth in crude oil demand, unconventional oil and gas resources become increasingly significant (Liu et al 2017, 2019). The relatively low resistance of silica nanofluids to temperature and salt aggravates the aggregation and precipitation after long-time use, which probably gives rise to the blockage of the pore-throats structure underground causing formation pollution (Das 2009). To overcome this problem, methods for preparing uniform and stable nanofluids are constantly developed (Li et al 2011; Babita and Gupta 2016), including physical and chemical modification methods (Esfandyari et al 2014; Arulprakasajothi et al 2015; Wu et al 2019). Zhou et al developed alumina polymerized olefin nanofluids by physical modification and the effects of shear
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